In recent years there has been tremendous interest and an increasing effort towards the development of biofuels made from lignocellulosic biomass derived from agricultural wastes, forest residues and dedicated energy crops. One of the largest limitations facing the overall economic viability of this process is the recalcitrance of biomass to enzymatic hydrolysis into its component sugars. This resistance to breakdown necessitates the use of a pretreatment step to enhance the accessibility to and hydrolysis of the carbohydrate components present. Most pretreatments are comprised of thermochemical processes that utilize combinations of high temperatures and pressures, or dilute acids or alkalis, to open up the structure of the biomass. This necessitates the use of specialized equipment and high-energy inputs.
Ionic liquids (ILs) have come into prominence over recent years used as innovative fluids for chemical processing. They are known as environmentally friendly solvents primarily due to their low volatility and their potential recyclability. Recently, the use of ILs for the pretreatment of biomass has been shown to be a promising technology, being able to solubilizing crystalline cellulose and biomass under relatively mild conditions. Reconstitution of the biomass from the IL results in an amorphous products that significantly increases the rate of enzymatic hydrolysis to its component sugars. The IL 1-ethyl-3-methylimidazolium acetate [C2Mim][OAc] has been found to be effective at the dissolution of biomass and the subsequent enhancement of enzymatic saccharification.
The ionic liquid pretreatment process can be generally described as the dissolution of biomass into the ionic liquid at temperature with stirring, followed by the addition of a precipitant that precipitates the biomass from solution. This precipitant is typically either water or ethanol or some other solvent with hydrogen bonding capacity. Once the biomass has been precipitated, solid liquid separation, and downstream enzymatic hydrolysis of the now amorphous biomass results in monosaccharides suitable for fermentation.
The proposed deconstruction process contains several steps that present themselves as points for maximizing sugar yields and cleaning up IL's for recycle. After the initial dissolution of the biomass in IL and precipitant addition, subsequent washings are required (Stage B in FIG. 9) for the recovery of amorphous biomass due to the low tolerance of commercial enzyme cocktails to ionic liquids. One possible way to reduce energy costs associated with precipitant removal and clean up, and extensive processing of the regenerated biomass to remove residual ILs is the development of cellulases that can perform optimally in the presence of ionic liquids. Successful development of IL tolerant cellulase provides potential candidates to be utilized for highly efficient deconstruction of biomass into monosaccharides in IL systems.
However, the removal of 5-carbon and 6-carbon monosaccharides from either an IL-free supernatant, pure IL or IL-aqueous solution remains a problem.